<!DOCTYPE HTML>
<html lang="zh-Hans" class="sidebar-visible no-js light">
    <head>
        <!-- Book generated using mdBook -->
        <meta charset="UTF-8">
        <title>数据库表达式执行的黑魔法：在Rust中用宏关联逻辑类型和实际类型 Part 7 - Rust 优秀博文</title>


        <!-- Custom HTML head -->
        
        <meta content="text/html; charset=utf-8" http-equiv="Content-Type">
        <meta name="description" content="">
        <meta name="viewport" content="width=device-width, initial-scale=1">
        <meta name="theme-color" content="#ffffff" />

        <link rel="icon" href="../../favicon.svg">
        <link rel="shortcut icon" href="../../favicon.png">
        <link rel="stylesheet" href="../../css/variables.css">
        <link rel="stylesheet" href="../../css/general.css">
        <link rel="stylesheet" href="../../css/chrome.css">
        <link rel="stylesheet" href="../../css/print.css" media="print">

        <!-- Fonts -->
        <link rel="stylesheet" href="../../FontAwesome/css/font-awesome.css">
        <link rel="stylesheet" href="../../fonts/fonts.css">

        <!-- Highlight.js Stylesheets -->
        <link rel="stylesheet" href="../../highlight.css">
        <link rel="stylesheet" href="../../tomorrow-night.css">
        <link rel="stylesheet" href="../../ayu-highlight.css">

        <!-- Custom theme stylesheets -->

    </head>
    <body>
        <!-- Provide site root to javascript -->
        <script type="text/javascript">
            var path_to_root = "../../";
            var default_theme = window.matchMedia("(prefers-color-scheme: dark)").matches ? "navy" : "light";
        </script>

        <!-- Work around some values being stored in localStorage wrapped in quotes -->
        <script type="text/javascript">
            try {
                var theme = localStorage.getItem('mdbook-theme');
                var sidebar = localStorage.getItem('mdbook-sidebar');

                if (theme.startsWith('"') && theme.endsWith('"')) {
                    localStorage.setItem('mdbook-theme', theme.slice(1, theme.length - 1));
                }

                if (sidebar.startsWith('"') && sidebar.endsWith('"')) {
                    localStorage.setItem('mdbook-sidebar', sidebar.slice(1, sidebar.length - 1));
                }
            } catch (e) { }
        </script>

        <!-- Set the theme before any content is loaded, prevents flash -->
        <script type="text/javascript">
            var theme;
            try { theme = localStorage.getItem('mdbook-theme'); } catch(e) { }
            if (theme === null || theme === undefined) { theme = default_theme; }
            var html = document.querySelector('html');
            html.classList.remove('no-js')
            html.classList.remove('light')
            html.classList.add(theme);
            html.classList.add('js');
        </script>

        <!-- Hide / unhide sidebar before it is displayed -->
        <script type="text/javascript">
            var html = document.querySelector('html');
            var sidebar = 'hidden';
            if (document.body.clientWidth >= 1080) {
                try { sidebar = localStorage.getItem('mdbook-sidebar'); } catch(e) { }
                sidebar = sidebar || 'visible';
            }
            html.classList.remove('sidebar-visible');
            html.classList.add("sidebar-" + sidebar);
        </script>

        <nav id="sidebar" class="sidebar" aria-label="Table of contents">
            <div class="sidebar-scrollbox">
                <ol class="chapter"><li class="chapter-item expanded "><a href="../../empty.html"><strong aria-hidden="true">1.</strong> 类型系统</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../../01_类型系统/Rust_Concept_Clarification_Deref_vs_AsRef_vs_Borrow_vs_Cow/Rust_Concept_Clarification_Deref_vs_AsRef_vs_Borrow_vs_Cow.html"><strong aria-hidden="true">1.1.</strong> Rust Concept Clarification Deref vs AsRef vs Borrow vs Cow</a></li><li class="chapter-item expanded "><a href="../../01_类型系统/Rust_Concept_Clarification_Deref_vs_AsRef_vs_Borrow_vs_Cow/Deref_AsRef_Borrow_Cow释义.html"><strong aria-hidden="true">1.2.</strong> Deref AsRef Borrow Cow 释义</a></li><li class="chapter-item expanded "><a href="../../01_类型系统/Rust的Borrow和AsRef：让你的代码用起来像呼吸一样自然/Rust的Borrow和AsRef：让你的代码用起来像呼吸一样自然.html"><strong aria-hidden="true">1.3.</strong> Rust的Borrow和AsRef：让你的代码用起来像呼吸一样自然</a></li><li class="chapter-item expanded "><a href="../../01_类型系统/Rust的Cow类型有什么用？详解Cow及其用途/Rust的Cow类型有什么用？详解Cow及其用途.html"><strong aria-hidden="true">1.4.</strong> Rust的Cow类型有什么用？详解Cow及其用途</a></li><li class="chapter-item expanded "><a href="../../01_类型系统/判别Fn、FnMut、FnOnce的标准/判别Fn、FnMut、FnOnce的标准.html"><strong aria-hidden="true">1.5.</strong> 判别Fn、FnMut、FnOnce的标准</a></li><li class="chapter-item expanded "><a href="../../01_类型系统/一行代码告诉你内部可变性的真相(UnsafeCell)/一行代码告诉你内部可变性的真相(UnsafeCell).html"><strong aria-hidden="true">1.6.</strong> 一行代码告诉你内部可变性的真相(UnsafeCell)</a></li><li class="chapter-item expanded "><a href="../../01_类型系统/Tour_of_Rust's_Standard_Library_Traits/Tour_of_Rust's_Standard_Library_Traits.html"><strong aria-hidden="true">1.7.</strong> Tour of Rust's Standard Library Traits</a></li><li class="chapter-item expanded "><a href="../../01_类型系统/逆变、协变与子类型，以及Rust/逆变、协变与子类型，以及Rust.html"><strong aria-hidden="true">1.8.</strong> 逆变、协变与子类型，以及Rust</a></li><li class="chapter-item expanded "><a href="../../01_类型系统/Rust自引用结构、Pin与Unpin/Rust自引用结构、Pin与Unpin.html"><strong aria-hidden="true">1.9.</strong> Rust自引用结构、Pin与Unpin</a></li><li class="chapter-item expanded "><a href="../../01_类型系统/为什么Rust需要Pin,Unpin/为什么Rust需要Pin,Unpin.html"><strong aria-hidden="true">1.10.</strong> 译：为什么 Rust 需要 Pin, Unpin ？</a></li><li class="chapter-item expanded "><a href="../../01_类型系统/定海神针Pin和Unpin/定海神针Pin和Unpin.html"><strong aria-hidden="true">1.11.</strong> 译：定海神针 Pin 和 Unpin</a></li><li class="chapter-item expanded "><a href="../../01_类型系统/sizedness-in-rust/sizedness-in-rust.html"><strong aria-hidden="true">1.12.</strong> Sizedness in Rust</a></li><li class="chapter-item expanded "><a href="../../01_类型系统/Rust生命周期集大成者PhantomData〈T〉/Rust生命周期集大成者PhantomData〈T〉.html"><strong aria-hidden="true">1.13.</strong> Rust生命周期集大成者 PhantomData&lt;T&gt;</a></li><li class="chapter-item expanded "><a href="../../01_类型系统/数据库表达式执行的黑魔法：用Rust做类型体操/数据库表达式执行的黑魔法：用Rust做类型体操_Part_0.html"><strong aria-hidden="true">1.14.</strong> 数据库表达式执行的黑魔法：用Rust做类型体操 Part 0</a></li><li class="chapter-item expanded "><a href="../../01_类型系统/数据库表达式执行的黑魔法：用Rust做类型体操/数据库表达式执行的黑魔法：GAT实现引用类型关联_Part_1.html"><strong aria-hidden="true">1.15.</strong> 数据库表达式执行的黑魔法：GAT实现引用类型关联 Part 1</a></li><li class="chapter-item expanded "><a href="../../01_类型系统/数据库表达式执行的黑魔法：用Rust做类型体操/数据库表达式执行的黑魔法：用HRTB写bound_Part_2.html"><strong aria-hidden="true">1.16.</strong> 数据库表达式执行的黑魔法：用HRTB写bound Part 2</a></li><li class="chapter-item expanded "><a href="../../01_类型系统/数据库表达式执行的黑魔法：用Rust做类型体操/数据库表达式执行的黑魔法：用Rust做类型体操之用宏展开重复代码_Part_3_&_4.html"><strong aria-hidden="true">1.17.</strong> 数据库表达式执行的黑魔法：用Rust做类型体操之用宏展开重复代码 Part 3 & 4</a></li><li class="chapter-item expanded "><a href="../../01_类型系统/数据库表达式执行的黑魔法：用Rust做类型体操/数据库表达式执行的黑魔法：与Rust编译器斗智斗勇之表达式向量化_Part_5_&_6.html"><strong aria-hidden="true">1.18.</strong> 数据库表达式执行的黑魔法：与Rust编译器斗智斗勇之表达式向量化 Part 5 & 6</a></li><li class="chapter-item expanded "><a href="../../01_类型系统/数据库表达式执行的黑魔法：用Rust做类型体操/数据库表达式执行的黑魔法：在Rust中用宏关联逻辑类型和实际类型_Part_7.html" class="active"><strong aria-hidden="true">1.19.</strong> 数据库表达式执行的黑魔法：在Rust中用宏关联逻辑类型和实际类型 Part 7</a></li></ol></li><li class="chapter-item expanded "><a href="../../empty.html"><strong aria-hidden="true">2.</strong> 生命周期</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../../02_生命周期/Rust中的生命周期——从StrSplit实例说开去/Rust中的生命周期——从StrSplit实例说开去.html"><strong aria-hidden="true">2.1.</strong> Rust中的生命周期——从StrSplit实例说开去</a></li><li class="chapter-item expanded "><a href="../../02_生命周期/与ChatGPT深度对话来学Rust生命周期/与ChatGPT深度对话来学Rust生命周期.html"><strong aria-hidden="true">2.2.</strong> 与ChatGPT深度对话来学Rust生命周期</a></li><li class="chapter-item expanded "><a href="../../02_生命周期/进击的Rust生命周期——early_bound与late_bound（1）/进击的Rust生命周期——early_bound与late_bound（1）.html"><strong aria-hidden="true">2.3.</strong> 进击的Rust生命周期——early_bound与late_bound（1）</a></li><li class="chapter-item expanded "><a href="../../02_生命周期/进击的Rust生命周期——early_bound与late_bound（2）/进击的Rust生命周期——early_bound与late_bound（2）.html"><strong aria-hidden="true">2.4.</strong> 进击的Rust生命周期——early_bound与late_bound（2）</a></li><li class="chapter-item expanded "><a href="../../02_生命周期/进击的Rust生命周期——一力降十会的MIR（1）/进击的Rust生命周期——一力降十会的MIR（1）.html"><strong aria-hidden="true">2.5.</strong> 进击的Rust生命周期——一力降十会的MIR（1）</a></li><li class="chapter-item expanded "><a href="../../02_生命周期/进击的Rust生命周期——一力降十会的MIR（2）/进击的Rust生命周期——一力降十会的MIR（2）.html"><strong aria-hidden="true">2.6.</strong> 进击的Rust生命周期——一力降十会的MIR（2）</a></li><li class="chapter-item expanded "><a href="../../02_生命周期/Common_Rust_Lifetime_Misconceptions/Common_Rust_Lifetime_Misconceptions.html"><strong aria-hidden="true">2.7.</strong> Common Rust Lifetime Misconceptions</a></li><li class="chapter-item expanded "><a href="../../02_生命周期/Rust生命周期常见误区/Rust生命周期常见误区.html"><strong aria-hidden="true">2.8.</strong> 译：Rust生命周期常见误区</a></li></ol></li><li class="chapter-item expanded "><a href="../../empty.html"><strong aria-hidden="true">3.</strong> 无畏并发</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../../05_无畏并发/简单写个Rust无锁队列/简单写个Rust无锁队列.html"><strong aria-hidden="true">3.1.</strong> 简单写个Rust无锁队列</a></li><li class="chapter-item expanded "><a href="../../05_无畏并发/进击的Rust多线程——混合自旋锁/进击的Rust多线程——混合自旋锁.html"><strong aria-hidden="true">3.2.</strong> 进击的Rust多线程——混合自旋锁</a></li><li class="chapter-item expanded "><a href="../../05_无畏并发/An_unsafe_tour_of_Rust's_Send_and_Sync/An_unsafe_tour_of_Rust's_Send_and_Sync.html"><strong aria-hidden="true">3.3.</strong> An unsafe tour of Rust's Send and Sync</a></li><li class="chapter-item expanded "><a href="../../05_无畏并发/进击的Rust多线程——Send与Sync/进击的Rust多线程——Send与Sync.html"><strong aria-hidden="true">3.4.</strong> 进击的Rust多线程——Send与Sync</a></li><li class="chapter-item expanded "><a href="../../05_无畏并发/进击的Rust多线程——离经叛道的PhantomData/进击的Rust多线程——离经叛道的PhantomData.html"><strong aria-hidden="true">3.5.</strong> 进击的Rust多线程——离经叛道的PhantomData</a></li><li class="chapter-item expanded "><a href="../../05_无畏并发/Rust_Async_Pin概念解析/Rust_Async_Pin概念解析.html"><strong aria-hidden="true">3.6.</strong> Rust Async: Pin概念解析</a></li><li class="chapter-item expanded "><a href="../../05_无畏并发/Rust和C++的并发库对比/Rust和C++的并发库对比.html"><strong aria-hidden="true">3.7.</strong> 译：Rust 和 C++ 的并发库对比</a></li><li class="chapter-item expanded "><a href="../../05_无畏并发/Rust原子类型和内存排序/Rust原子类型和内存排序.html"><strong aria-hidden="true">3.8.</strong> Rust原子类型和内存排序</a></li></ol></li><li class="chapter-item expanded "><a href="../../empty.html"><strong aria-hidden="true">4.</strong> 网络编程</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../../06_网络编程/从编解码层面理解WebSocket_手写一个WebSocket/从编解码层面理解WebSocket_手写一个WebSocket.html"><strong aria-hidden="true">4.1.</strong> 从编解码层面理解WebSocket 手写一 个WebSocket</a></li><li class="chapter-item expanded "><a href="../../06_网络编程/透过Rust探索系统的本原：网络篇/透过Rust探索系统的本原：网络篇.html"><strong aria-hidden="true">4.2.</strong> 透过Rust探索系统的本原：网络篇</a></li></ol></li><li class="chapter-item expanded "><a href="../../empty.html"><strong aria-hidden="true">5.</strong> 轮子系列</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../../07_轮子系列/700行Rust写一个内存分配器/700行Rust写一个内存分配器.html"><strong aria-hidden="true">5.1.</strong> 700行Rust写一个内存分配器</a></li><li class="chapter-item expanded "><a href="../../07_轮子系列/Rust：网络库的实现思路/Rust：网络库的实现思路.html"><strong aria-hidden="true">5.2.</strong> Rust：网络库的实现思路</a></li><li class="chapter-item expanded "><a href="../../07_轮子系列/Rust异步运行时基础部件/Rust异步运行时基础部件.html"><strong aria-hidden="true">5.3.</strong> Rust异步运行时基础部件</a></li><li class="chapter-item expanded "><a href="../../07_轮子系列/使用Rust+epoll编写异步IO框架/使用Rust+epoll编写异步IO框架（1）.html"><strong aria-hidden="true">5.4.</strong> 使用Rust+epoll编写异步IO框架（1）</a></li><li class="chapter-item expanded "><a href="../../07_轮子系列/使用Rust+epoll编写异步IO框架/使用Rust+epoll编写异步IO框架（2）.html"><strong aria-hidden="true">5.5.</strong> 使用Rust+epoll编写异步IO框架（2）</a></li><li class="chapter-item expanded "><a href="../../07_轮子系列/使用Rust+epoll编写异步IO框架/使用Rust+epoll编写异步IO框架（3）.html"><strong aria-hidden="true">5.6.</strong> 使用Rust+epoll编写异步IO框架（3）</a></li><li class="chapter-item expanded "><a href="../../07_轮子系列/用rust从零开发一套web框架/用rust从零开发一套web框架：day1.html"><strong aria-hidden="true">5.7.</strong> 用rust从零开发一套web框架：day1</a></li><li class="chapter-item expanded "><a href="../../07_轮子系列/用rust从零开发一套web框架/用rust从零开发一套web框架：day2.html"><strong aria-hidden="true">5.8.</strong> 用rust从零开发一套web框架：day2</a></li><li class="chapter-item expanded "><a href="../../07_轮子系列/用rust从零开发一套web框架/用rust从零开发一套web框架：day3.html"><strong aria-hidden="true">5.9.</strong> 用rust从零开发一套web框架：day3</a></li><li class="chapter-item expanded "><a href="../../07_轮子系列/用rust从零开发一套web框架/用rust从零开发一套web框架：day4.html"><strong aria-hidden="true">5.10.</strong> 用rust从零开发一套web框架：day4</a></li><li class="chapter-item expanded "><a href="../../07_轮子系列/用rust从零开发一套web框架/用rust从零开发一套web框架：day5.html"><strong aria-hidden="true">5.11.</strong> 用rust从零开发一套web框架：day5</a></li></ol></li><li class="chapter-item expanded "><a href="../../empty.html"><strong aria-hidden="true">6.</strong> 奇技淫巧</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../../08_奇技淫巧/Copy-On-Write是不是优化？/Copy-On-Write是不是优化？.html"><strong aria-hidden="true">6.1.</strong> 译：Copy-On-Write是不是优化？</a></li><li class="chapter-item expanded "><a href="../../08_奇技淫巧/揭秘神奇的Rust_Axum风格的函数实现/揭秘神奇的Rust_Axum风格的函数实现.html"><strong aria-hidden="true">6.2.</strong> 译：揭秘神奇的 Rust Axum 风格的函数实现</a></li><li class="chapter-item expanded "><a href="../../08_奇技淫巧/“变长参数”函数与回调/“变长参数”函数与回调.html"><strong aria-hidden="true">6.3.</strong> “变长参数”函数与回调</a></li><li class="chapter-item expanded "><a href="../../08_奇技淫巧/Rust字符串格式化的幕后：format_args!()/Rust字符串格式化的幕后：format_args!().html"><strong aria-hidden="true">6.4.</strong> 译：Rust字符串格式化的幕后：format_args!()</a></li><li class="chapter-item expanded "><a href="../../08_奇技淫巧/给Rust带来一点C++特产/给Rust带来一点C++特产.html"><strong aria-hidden="true">6.5.</strong> 给Rust带来一点C++特产</a></li><li class="chapter-item expanded "><a href="../../08_奇技淫巧/一步步实现_Rust_Bevy_ECS_的_System_简化版本/一步步实现_Rust_Bevy_ECS_的_System_简化版本.html"><strong aria-hidden="true">6.6.</strong> 一步步实现 Rust Bevy ECS 的 System 简化版本</a></li><li class="chapter-item expanded "><a href="../../08_奇技淫巧/Exploring_Design_Patterns_in_Rust_with_Algorithmic_Trading_Examples/Exploring_Design_Patterns_in_Rust_with_Algorithmic_Trading_Examples.html"><strong aria-hidden="true">6.7.</strong> Exploring Design Patterns in Rust with Algorithmic Trading Examples</a></li></ol></li><li class="chapter-item expanded "><a href="../../empty.html"><strong aria-hidden="true">7.</strong> 源码分析</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../../09_源码分析/Rust并发：bytes源码分析/Rust并发：bytes源码分析.html"><strong aria-hidden="true">7.1.</strong> Rust并发：bytes源码分析</a></li><li class="chapter-item expanded "><a href="../../09_源码分析/Rust并发：标准库Arc源码分析/Rust并发：标准库Arc源码分析.html"><strong aria-hidden="true">7.2.</strong> Rust并发：标准库Arc源码分析</a></li><li class="chapter-item expanded "><a href="../../09_源码分析/Rust并发：标准库sync_Once源码分析/Rust并发：标准库sync_Once源码分析.html"><strong aria-hidden="true">7.3.</strong> Rust并发：标准库sync::Once源码分析</a></li><li class="chapter-item expanded "><a href="../../09_源码分析/Rust源码阅读：引用计数Rc/Rust源码阅读：引用计数Rc.html"><strong aria-hidden="true">7.4.</strong> Rust源码阅读：引用计数Rc</a></li><li class="chapter-item expanded "><a href="../../09_源码分析/Rust源码阅读：Cell、RefCell与内部可变性/Rust源码阅读：Cell、RefCell与内部可变性.html"><strong aria-hidden="true">7.5.</strong> Rust源码阅读： Cell、RefCell与内部可变性</a></li><li class="chapter-item expanded "><a href="../../09_源码分析/关于_Rust_的_UnsafeCell、Cell_与_RefCell/关于_Rust_的_UnsafeCell、Cell_与_RefCell.html"><strong aria-hidden="true">7.6.</strong> 关于 Rust 的 UnsafeCell、Cell 与 RefCell</a></li><li class="chapter-item expanded "><a href="../../09_源码分析/Rust_Async_async-stream源码分析/Rust_Async_async-stream源码分析.html"><strong aria-hidden="true">7.7.</strong> Rust Async: async-stream源码分析</a></li><li class="chapter-item expanded "><a href="../../09_源码分析/走进Tokio的异步世界/走进Tokio的异步世界.html"><strong aria-hidden="true">7.8.</strong> 走进 Tokio 的异步世界</a></li><li class="chapter-item expanded "><a href="../../09_源码分析/tokio.rs_runtime的实现/tokio.rs_runtime的实现.html"><strong aria-hidden="true">7.9.</strong> tokio.rs runtime 的实现</a></li><li class="chapter-item expanded "><a href="../../09_源码分析/Tokio_internals/Tokio_internals.html"><strong aria-hidden="true">7.10.</strong> Tokio internals</a></li><li class="chapter-item expanded "><a href="../../09_源码分析/Tokio_internals/译文：Tokio內部机制.html"><strong aria-hidden="true">7.11.</strong> 译：Tokio 内部机制</a></li><li class="chapter-item expanded "><a href="../../09_源码分析/Rust_Axum_HTTP_框架的架构分析/Rust_Axum_HTTP_框架的架构分析.html"><strong aria-hidden="true">7.12.</strong> Rust Axum HTTP 框架的架构分析</a></li><li class="chapter-item expanded "><a href="../../09_源码分析/安利一个Rust_Game_Engine：Bevy--ECS部分/安利一个Rust_Game_Engine：Bevy--ECS部分.html"><strong aria-hidden="true">7.13.</strong> 安利一个Rust Game Engine：Bevy--ECS部分</a></li><li class="chapter-item expanded "><a href="../../09_源码分析/Tokio_解析之任务调度/Tokio_解析之任务调度.html"><strong aria-hidden="true">7.14.</strong> Tokio 解析之任务调度</a></li></ol></li><li class="chapter-item expanded "><a href="../../empty.html"><strong aria-hidden="true">8.</strong> 生态观察</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../../11_生态观察/Rust_web_frameworks_have_subpar_error_reporting/Rust_web_frameworks_have_subpar_error_reporting.html"><strong aria-hidden="true">8.1.</strong> Rust web frameworks have subpar error reporting</a></li><li class="chapter-item expanded "><a href="../../11_生态观察/SeaORM：要做Rust版本的ActiveRecord/SeaORM：要做Rust版本的ActiveRecord.html"><strong aria-hidden="true">8.2.</strong> SeaORM：要做Rust版本的ActiveRecord</a></li></ol></li><li class="chapter-item expanded "><a href="../../empty.html"><strong aria-hidden="true">9.</strong> 死灵终极</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../../12_死灵终极/Learn_Rust_the_Dangerous_Way_系列文章翻译/Learn_Rust_the_Dangerous_Way_系列文章翻译_总述.html"><strong aria-hidden="true">9.1.</strong> 译：Learn Rust the Dangerous Way 总述</a></li><li class="chapter-item expanded "><a href="../../12_死灵终极/Learn_Rust_the_Dangerous_Way_系列文章翻译/Learn_Rust_the_Dangerous_Way_系列文章翻译_0.html"><strong aria-hidden="true">9.2.</strong> 译：Learn Rust the Dangerous Way 0</a></li><li class="chapter-item expanded "><a href="../../12_死灵终极/Learn_Rust_the_Dangerous_Way_系列文章翻译/Learn_Rust_the_Dangerous_Way_系列文章翻译_1.html"><strong aria-hidden="true">9.3.</strong> 译：Learn Rust the Dangerous Way 1</a></li><li class="chapter-item expanded "><a href="../../12_死灵终极/Learn_Rust_the_Dangerous_Way_系列文章翻译/Learn_Rust_the_Dangerous_Way_系列文章翻译_2.html"><strong aria-hidden="true">9.4.</strong> 译：Learn Rust the Dangerous Way 2</a></li><li class="chapter-item expanded "><a href="../../12_死灵终极/Learn_Rust_the_Dangerous_Way_系列文章翻译/Learn_Rust_the_Dangerous_Way_系列文章翻译_3.html"><strong aria-hidden="true">9.5.</strong> 译：Learn Rust the Dangerous Way 3</a></li><li class="chapter-item expanded "><a href="../../12_死灵终极/Learn_Rust_the_Dangerous_Way_系列文章翻译/Learn_Rust_the_Dangerous_Way_系列文章翻译_4.html"><strong aria-hidden="true">9.6.</strong> 译：Learn Rust the Dangerous Way 4</a></li><li class="chapter-item expanded "><a href="../../12_死灵终极/Learn_Rust_the_Dangerous_Way_系列文章翻译/Learn_Rust_the_Dangerous_Way_系列文章翻译_5.html"><strong aria-hidden="true">9.7.</strong> 译：Learn Rust the Dangerous Way 5</a></li><li class="chapter-item expanded "><a href="../../12_死灵终极/Unsafe_Rust_随堂小测/Unsafe_Rust_随堂小测（一）.html"><strong aria-hidden="true">9.8.</strong> Unsafe Rust 随堂小测（一）</a></li><li class="chapter-item expanded "><a href="../../12_死灵终极/Unsafe_Rust_随堂小测/Unsafe_Rust_随堂小测（二）.html"><strong aria-hidden="true">9.9.</strong> Unsafe Rust 随堂小测（二）</a></li><li class="chapter-item expanded "><a href="../../12_死灵终极/Unsafe_Rust_随堂小测/Unsafe_Rust_随堂小测（三）.html"><strong aria-hidden="true">9.10.</strong> Unsafe Rust 随堂小测（三）</a></li><li class="chapter-item expanded "><a href="../../12_死灵终极/Unsafe_Rust_随堂小测/Unsafe_Rust_随堂小测参考答案.html"><strong aria-hidden="true">9.11.</strong> Unsafe Rust 随堂小测参考答案</a></li></ol></li></ol>
            </div>
            <div id="sidebar-resize-handle" class="sidebar-resize-handle"></div>
        </nav>

        <div id="page-wrapper" class="page-wrapper">

            <div class="page">
                                <div id="menu-bar-hover-placeholder"></div>
                <div id="menu-bar" class="menu-bar sticky bordered">
                    <div class="left-buttons">
                        <button id="sidebar-toggle" class="icon-button" type="button" title="Toggle Table of Contents" aria-label="Toggle Table of Contents" aria-controls="sidebar">
                            <i class="fa fa-bars"></i>
                        </button>
                        <button id="theme-toggle" class="icon-button" type="button" title="Change theme" aria-label="Change theme" aria-haspopup="true" aria-expanded="false" aria-controls="theme-list">
                            <i class="fa fa-paint-brush"></i>
                        </button>
                        <ul id="theme-list" class="theme-popup" aria-label="Themes" role="menu">
                            <li role="none"><button role="menuitem" class="theme" id="light">Light (default)</button></li>
                            <li role="none"><button role="menuitem" class="theme" id="rust">Rust</button></li>
                            <li role="none"><button role="menuitem" class="theme" id="coal">Coal</button></li>
                            <li role="none"><button role="menuitem" class="theme" id="navy">Navy</button></li>
                            <li role="none"><button role="menuitem" class="theme" id="ayu">Ayu</button></li>
                        </ul>
                        <button id="search-toggle" class="icon-button" type="button" title="Search. (Shortkey: s)" aria-label="Toggle Searchbar" aria-expanded="false" aria-keyshortcuts="S" aria-controls="searchbar">
                            <i class="fa fa-search"></i>
                        </button>
                    </div>

                    <h1 class="menu-title">Rust 优秀博文</h1>

                    <div class="right-buttons">
                        <a href="../../print.html" title="Print this book" aria-label="Print this book">
                            <i id="print-button" class="fa fa-print"></i>
                        </a>

                    </div>
                </div>

                <div id="search-wrapper" class="hidden">
                    <form id="searchbar-outer" class="searchbar-outer">
                        <input type="search" id="searchbar" name="searchbar" placeholder="Search this book ..." aria-controls="searchresults-outer" aria-describedby="searchresults-header">
                    </form>
                    <div id="searchresults-outer" class="searchresults-outer hidden">
                        <div id="searchresults-header" class="searchresults-header"></div>
                        <ul id="searchresults">
                        </ul>
                    </div>
                </div>

                <!-- Apply ARIA attributes after the sidebar and the sidebar toggle button are added to the DOM -->
                <script type="text/javascript">
                    document.getElementById('sidebar-toggle').setAttribute('aria-expanded', sidebar === 'visible');
                    document.getElementById('sidebar').setAttribute('aria-hidden', sidebar !== 'visible');
                    Array.from(document.querySelectorAll('#sidebar a')).forEach(function(link) {
                        link.setAttribute('tabIndex', sidebar === 'visible' ? 0 : -1);
                    });
                </script>

                <div id="content" class="content">
                    <main>
                        <h1 id="数据库表达式执行的黑魔法在-rust-中用宏关联逻辑类型和实际类型-part-7"><a class="header" href="#数据库表达式执行的黑魔法在-rust-中用宏关联逻辑类型和实际类型-part-7">数据库表达式执行的黑魔法：在 Rust 中用宏关联逻辑类型和实际类型 (Part 7)</a></h1>
<p>作者：<a href="https://www.zhihu.com/people/skyzh">迟策</a></p>
<p>原载：<a href="https://zhuanlan.zhihu.com/p/463477290">https://zhuanlan.zhihu.com/p/463477290</a></p>
<p>上篇：<a href="https://zhuanlan.zhihu.com/p/461901665">数据库表达式执行的黑魔法：与 Rust 编译器斗智斗勇 (Part 5 &amp; 6)</a></p>
<h2 id="day-7-用宏关联逻辑类型和实际类型"><a class="header" href="#day-7-用宏关联逻辑类型和实际类型">Day 7: 用宏关联逻辑类型和实际类型</a></h2>
<p>在数据库系统中，逻辑类型和实际存储的类型往往不会是一一对应的关系。举例，<code>CHAR</code> 和 <code>VARCHAR</code> 是两种不同的逻辑类型，但大多数数据库系统对于这两种类型都会用同一种内存表示。在前几天的类型体操中，我们实现的类型都是实际类型 (Physical Type)。在今天，我们将会把逻辑类型和实际类型关联起来，并批量生成表达式。</p>
<h3 id="目标"><a class="header" href="#目标">目标</a></h3>
<p>之前我们实现了 <code>cmp_ge</code> 这个函数，可以将两个输入 cast 成一个指定类型后进行比较。如何生成所有支持类型的 <code>cmp_ge</code> 函数呢？正常来说，我们可能需要：</p>
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>pub fn build_binary_expression(
    f: ExpressionFunc,
    i1: DataType,
    i2: DataType,
) -&gt; Box&lt;dyn Expression&gt; {
    use ExpressionFunc::*;

    use crate::expr::cmp::*;
    use crate::expr::string::*;

    match f {
        CmpLe =&gt; match (i1, i2) {
            (DataType::BigInt, DataType::Integer) =&gt; Box::new(
                BinaryExpression::&lt;i64, i32, bool, _&gt;::new(cmp_le::&lt;i64, i32, i64&gt;),
            ),
            (DataType::Integer, DataType::BigInt) =&gt; Box::new(
                BinaryExpression::&lt;i32, i64, bool, _&gt;::new(cmp_le::&lt;i32, i64, i64&gt;),
            ),
            _ =&gt; unimplemented!(),
        },
        _ =&gt; unimplemented!(),
    }
}
<span class="boring">}
</span></code></pre></pre>
<p>如此枚举所有的可能。想想我们的系统里面，现在一共有 8 种类型，于是乎这里可能要写 8 * 8 = 64 个 arm。每个 arm 都要将逻辑类型 <code>DataType</code> 和实际类型 <code>i32</code> 匹配起来，并指定 cast 的目标，很容易写错。</p>
<p>大家可能立刻可以想到，能不能用 associated type 来表示这些类型之间的关系呢？显然不行。其一，<code>DataType</code> 是一个 enum，里面的每个 variant 没有自己的类型，不能直接关联。其二，像 <code>CHAR</code>, <code>Decimal</code> 这种逻辑类型，往往会带上一些附加信息。比如 <code>CHAR</code> 的长度、<code>Decimal</code> 的精度等等。这样一来，根本没有办法使用 generic 提供的工具来进行逻辑类型和实际类型之间的关联。</p>
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>/// Encapsules all supported (logical) data types in the system.
#[derive(Debug)]
pub enum DataType {
    /// Corresponding to Int16 physical type
    SmallInt,
    /// Corresponding to Int32 physical type
    Integer,
    /// Corresponding to Int64 physical type
    BigInt,
    /// Corresponding to String physical type
    Varchar,
    /// Corresponding to String physical type
    Char { width: u16 },
    /// Corresponding to Bool physical type
    Boolean,
    /// Corresponding to Float32 physical type
    Real,
    /// Corresponding to Float64 physical type
    Double,
    /// Corresponding to Decimal physical type
    Decimal { scale: u16, precision: u16 },
}
<span class="boring">}
</span></code></pre></pre>
<p>而我们的目标，是将 <code>build_expression</code> 写成这种形式：</p>
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>/// Build expression with runtime information.
pub fn build_binary_expression(
    f: ExpressionFunc,
    i1: DataType,
    i2: DataType,
) -&gt; Box&lt;dyn Expression&gt; {
    use ExpressionFunc::*;

    use crate::expr::cmp::*;
    use crate::expr::string::*;

    match f {
        CmpLe =&gt; for_all_cmp_combinations! { impl_cmp_expression_of, i1, i2, cmp_le },
        CmpGe =&gt; for_all_cmp_combinations! { impl_cmp_expression_of, i1, i2, cmp_ge },
        CmpEq =&gt; for_all_cmp_combinations! { impl_cmp_expression_of, i1, i2, cmp_eq },
        CmpNe =&gt; for_all_cmp_combinations! { impl_cmp_expression_of, i1, i2, cmp_ne },
        StrContains =&gt; Box::new(BinaryExpression::&lt;String, String, bool, _&gt;::new(
            str_contains,
        )),
    }
}
<span class="boring">}
</span></code></pre></pre>
<p>怎么办捏？</p>
<h3 id="用-macro-关联逻辑类型和实际类型"><a class="header" href="#用-macro-关联逻辑类型和实际类型">用 macro 关联逻辑类型和实际类型</a></h3>
<p>在 Day 3 中我们已经讲过 Rust 声明宏的特殊性：它的展开顺序是由外到里的。在这种情况下，我们如何定义 <code>DataType</code> 到实际类型的映射呢？</p>
<p>一种办法就是用类似于下面这种回调的方式：</p>
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>/// Association information for `Boolean` logical type.
macro_rules! boolean {
    ($macro:ident) =&gt; {
        $macro! {
            DataType::Boolean,
            BoolArray,
            bool
        }
    };
}

pub(crate) use boolean;
<span class="boring">}
</span></code></pre></pre>
<p><code>boolean</code> 这个 macro 包含了 <code>DataType::Boolean</code> 的所有信息——它的逻辑类型是 Boolean，对应的 Array 类型是 <code>BoolArray</code>，标量类型是 <code>bool</code>。</p>
<p>再看一个例子：</p>
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>/// Association information for `Char` logical type.
macro_rules! fwchar {
    ($macro:ident) =&gt; {
        $macro! {
            DataType::Char { .. },
            StringArray,
            String
        }
    };
}

pub(crate) use fwchar;
<span class="boring">}
</span></code></pre></pre>
<p><code>fwchar</code> 这个逻辑类型对应的 match pattern 是 <code>DataType::Char { .. }</code>，它可以出现在 match arm 里面。对应的 Array 类型是 <code>StringArray</code>，标量类型是 <code>String</code>。</p>
<p>接下来，使用者如何把里面的内容提出来捏？我们定义三个宏，分别 extract 里面的每一个元素：</p>
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>/// Get the type match pattern out of the type macro. e.g., `DataTypeKind::Decimal { .. }`.
macro_rules! datatype_match_pattern {
    ($match_pattern:pat, $array:ty, $scalar:ty) =&gt; {
        $match_pattern
    };
}

pub(crate) use datatype_match_pattern;

/// Get the array type out of the type macro. e.g., `Int32Array`.
macro_rules! datatype_array {
    ($match_pattern:pat, $array:ty, $scalar:ty) =&gt; {
        $array
    };
}

pub(crate) use datatype_array;

/// Get the scalar type out of the type macro. e.g., `i32`.
macro_rules! datatype_scalar {
    ($match_pattern:pat, $array:ty, $scalar:ty) =&gt; {
        $scalar
    };
}

pub(crate) use datatype_scalar;
<span class="boring">}
</span></code></pre></pre>
<p>这样一来，我们就可以用 <code>fwchar! { datatype_match_pattern };</code> 来得到定义在 <code>fwchar</code> 宏里面的 <code>DataType::Char { .. }</code> 了。</p>
<p>用 <code>trace_macro</code> 看一下结果：</p>
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>fn test_macro_expand() {
    trace_macros!(true);
    fwchar! { datatype_match_pattern };
    boolean! { datatype_array };
    decimal! { datatype_scalar };
    trace_macros!(false);
}

note: trace_macro
   --&gt; src/datatype/macros.rs:164:5
    |
164 |     boolean! { datatype_array };
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: expanding `boolean! { datatype_array }`
    = note: to `datatype_array! { DataType :: Boolean, BoolArray, bool }`
    = note: expanding `datatype_array! { DataType :: Boolean, BoolArray, bool }`
    = note: to `BoolArray`

note: trace_macro
   --&gt; src/datatype/macros.rs:163:5
    |
163 |     fwchar! { datatype_match_pattern };
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: expanding `fwchar! { datatype_match_pattern }`
    = note: to `datatype_match_pattern! { DataType :: Char { .. }, StringArray, String }`
    = note: expanding `datatype_match_pattern! { DataType :: Char { .. }, StringArray, String }`
    = note: to `DataType::Char { .. }`

note: trace_macro
   --&gt; src/datatype/macros.rs:165:5
    |
165 |     decimal! { datatype_scalar };
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: expanding `decimal! { datatype_scalar }`
    = note: to `datatype_scalar!
            { DataType :: Decimal { .. }, DecimalArray, rust_decimal :: Decimal }`
    = note: expanding `datatype_scalar! { DataType :: Decimal { .. }, DecimalArray, rust_decimal :: Decimal }`
    = note: to `rust_decimal::Decimal`
<span class="boring">}
</span></code></pre></pre>
<p>可以看到三句话分别展开成了 <code>BoolArray</code>, <code>DataType::Char { .. }</code>, <code>Decimal</code>, 正好可以用在 <code>build_expression</code> 里面。</p>
<h3 id="展开所有比较函数"><a class="header" href="#展开所有比较函数">展开所有比较函数</a></h3>
<p>接下来我们借助类型体操 Day 3, 4 里面的技巧，用 <code>for_all_cmp_combinations</code> 和 <code>impl_cmp_expression_of</code> 这一对 macro 来展开所有的比较函数。</p>
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>/// Composes all combinations of possible comparisons
///
/// Each item in the list `{ a, b, c }` represents:
/// * 1st position: left input type.
/// * 2nd position: right input type.
/// * 3rd position: cast type. For example, we need to cast the left i32 to i64 before comparing i32
///   and i64.
macro_rules! for_all_cmp_combinations {
    ($macro:tt $(, $x:tt)*) =&gt; {
        $macro! {
            [$($x),*],
            // comparison for the same type
            { int16, int16, int16 },
            { int32, int32, int32 },
            { int64, int64, int64 },
            { float32, float32, float32 },
            { float64, float64, float64 },
            { decimal, decimal, decimal },
            { fwchar, fwchar, fwchar },
            { varchar, varchar, varchar },
            // comparison across integer types
            { int16, int32, int32 },
            { int32, int16, int32 },
            { int16, int64, int64 },
            { int32, int64, int64 },
            { int64, int16, int64 },
            { int64, int32, int64 },
            // comparison across float types
            { float32, float64, float64 },
            { float64, float32, float64 },
            // comparison across integer and float32 types
            { int16, float32, float32 },
            { float32, int16, float32 },
            { int32, float32, float64 },
            { float32, int32, float64 },
            // comparison across integer and float64 types
            { int32, float64, float64 },
            { float64, int32, float64 },
            { int16, float64, float64 },
            { float64, int16, float64 },
            // comparison with decimal types
            { int16, decimal, decimal },
            { decimal, int16, decimal },
            { int32, decimal, decimal },
            { decimal, int32, decimal },
            { int64, decimal, decimal },
            { decimal, int64, decimal }
        }
    };
}
<span class="boring">}
</span></code></pre></pre>
<p>我们使用 <code>for_all_cmp_combinations</code> 这个 macro 来声明所有可以比较的数据类型。以 <code>{ int16, float32, float32 }</code> 这一行为例，它的意思就是 int16 和 float32 可以进行比较，比较前 cast 到 float32 类型。</p>
<p>然后我们考虑一下 <code>impl_cmp_expression_of</code> 这个 macro 怎么实现。回到最开始写的一段代码：</p>
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>(DataType::BigInt, DataType::Integer) =&gt; Box::new(
    BinaryExpression::&lt;i64, i32, bool, _&gt;::new(cmp_le::&lt;i64, i32, i64&gt;),
),
<span class="boring">}
</span></code></pre></pre>
<p>一拍脑袋，所有用到类型的地方都可以用 macro 来改写。假设输入的两个类型分别是 <code>$i1</code> 和 <code>$i2</code>，需要 cast 成 <code>$convert</code> 类型。先看 match arm：</p>
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>(DataType::BigInt, DataType::Integer) =&gt;
// ... can be rewritten to
($i1! { datatype_match_pattern }, $i2! { datatype_match_pattern }) =&gt;
<span class="boring">}
</span></code></pre></pre>
<p>然后看看 BinaryExpression 这一段：</p>
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>Box::new(
    BinaryExpression::&lt;i64, i32, bool, _&gt;::new(cmp_le::&lt;i64, i32, i64&gt;),
)
// ... can be rewritten to
Box::new(BinaryExpression::&lt;
    $i1! { datatype_scalar },
    $i2! { datatype_scalar },
    bool,
    _
&gt;::new(
    $cmp_func::&lt;
        $i1! { datatype_scalar },
        $i2! { datatype_scalar },
        $convert! { datatype_scalar }
    &gt;,
))
<span class="boring">}
</span></code></pre></pre>
<p>这样就得到了 <code>impl_cmp_expression_of</code> 的实现：</p>
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>macro_rules! impl_cmp_expression_of {
    ([$i1t:ident, $i2t:ident, $cmp_func:tt], $({ $i1:tt, $i2:tt, $convert:tt }),*) =&gt; {
        match ($i1t, $i2t) {
            $(
                ($i1! { datatype_match_pattern }, $i2! { datatype_match_pattern }) =&gt; {
                    Box::new(BinaryExpression::&lt;
                        $i1! { datatype_scalar },
                        $i2! { datatype_scalar },
                        bool,
                        _
                    &gt;::new(
                        $cmp_func::&lt;
                            $i1! { datatype_scalar },
                            $i2! { datatype_scalar },
                            $convert! { datatype_scalar }
                        &gt;,
                    ))
                }
            )*
            (other_dt1, other_dt2) =&gt; unimplemented!(&quot;unsupported comparison: {:?} &lt;{}&gt; {:?}&quot;,
                other_dt1,
                stringify!($cmp_func),
                other_dt2)
        }
    };
}
<span class="boring">}
</span></code></pre></pre>
<p>最后，在 <code>build_expression</code> 里面用宏展开：</p>
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>/// Build expression with runtime information.
pub fn build_binary_expression(
    f: ExpressionFunc,
    i1: DataType,
    i2: DataType,
) -&gt; Box&lt;dyn Expression&gt; {
    use ExpressionFunc::*;

    use crate::expr::cmp::*;
    use crate::expr::string::*;

    match f {
        CmpLe =&gt; for_all_cmp_combinations! { impl_cmp_expression_of, i1, i2, cmp_le },
        CmpGe =&gt; for_all_cmp_combinations! { impl_cmp_expression_of, i1, i2, cmp_ge },
        CmpEq =&gt; for_all_cmp_combinations! { impl_cmp_expression_of, i1, i2, cmp_eq },
        CmpNe =&gt; for_all_cmp_combinations! { impl_cmp_expression_of, i1, i2, cmp_ne },
        StrContains =&gt; Box::new(BinaryExpression::&lt;String, String, bool, _&gt;::new(
            str_contains,
        )),
    }
}
<span class="boring">}
</span></code></pre></pre>
<p>由此，我们用简单的代码，实现了任何两种类型比较函数的向量化。Day 7 结束了！</p>
<p>上篇：<a href="https://zhuanlan.zhihu.com/p/461901665">数据库表达式执行的黑魔法：与 Rust 编译器斗智斗勇 (Part 5 &amp; 6)</a></p>
<p>您可以在 <a href="https://link.zhihu.com/?target=https%3A//github.com/skyzh/type-exercise-in-rust">type-exercise-in-rust</a> 中围观整个系统的实现。</p>
<p><em>（系列文章持续更新中，下一次更新时间看心情）</em></p>
<p>编辑于 2022-02-02 16:11</p>

                    </main>

                    <nav class="nav-wrapper" aria-label="Page navigation">
                        <!-- Mobile navigation buttons -->
                            <a rel="prev" href="../../01_类型系统/数据库表达式执行的黑魔法：用Rust做类型体操/数据库表达式执行的黑魔法：与Rust编译器斗智斗勇之表达式向量化_Part_5_&amp;_6.html" class="mobile-nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
                                <i class="fa fa-angle-left"></i>
                            </a>

                            <a rel="next" href="../../empty.html" class="mobile-nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
                                <i class="fa fa-angle-right"></i>
                            </a>

                        <div style="clear: both"></div>
                    </nav>
                </div>
            </div>

            <nav class="nav-wide-wrapper" aria-label="Page navigation">
                    <a rel="prev" href="../../01_类型系统/数据库表达式执行的黑魔法：用Rust做类型体操/数据库表达式执行的黑魔法：与Rust编译器斗智斗勇之表达式向量化_Part_5_&amp;_6.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
                        <i class="fa fa-angle-left"></i>
                    </a>

                    <a rel="next" href="../../empty.html" class="nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
                        <i class="fa fa-angle-right"></i>
                    </a>
            </nav>

        </div>




        <script type="text/javascript">
            window.playground_copyable = true;
        </script>


        <script src="../../elasticlunr.min.js" type="text/javascript" charset="utf-8"></script>
        <script src="../../mark.min.js" type="text/javascript" charset="utf-8"></script>
        <script src="../../searcher.js" type="text/javascript" charset="utf-8"></script>

        <script src="../../clipboard.min.js" type="text/javascript" charset="utf-8"></script>
        <script src="../../highlight.js" type="text/javascript" charset="utf-8"></script>
        <script src="../../book.js" type="text/javascript" charset="utf-8"></script>

        <!-- Custom JS scripts -->


    </body>
</html>
